# Homework Help: Formula to solve this question

1. Jan 1, 2007

### hisoko

Hi i need to know the formula to solve this question

stone is thrown off cliff horizontally at a speed ??m/s from the top of a cliff thats ??m high. How do i find the time it takes for the stone to touch the ground?

2. Jan 1, 2007

### billiards

the horizontal speed doesn't matter,

t=(2d/g)0.5

t is time
d is distance
g is acceleration due to gravity

Last edited: Jan 1, 2007
3. Jan 1, 2007

### theperthvan

Horizontal and vertical velocities and treated separately. So Throwing it horizontally is like dropping it straight down when from a vertical point of view.

s=ut + 1/2 *a*t^2

s-distance it falls (height of cliff)
u-initial velocity = 0 => ut=0
a-gravity (g)

so...t=(2s/g)^(1/2)

4. Jan 1, 2007

### hisoko

okay and to find the displacment? (distance from the base of the cliff to where the stone lands) from knowing only the height of cliff and speed of rock

5. Jan 1, 2007

### cristo

Staff Emeritus
It is against PF rules to give answers to homework questions. Try googling "kinematic equations" and post back your thoughts on the question, and we will be able to help you further. In future, please use the template with which you were provided:

6. Jan 1, 2007

### turdferguson

You know the horizontal velocity (which is constant throughout) and you just figured out how long it is going to travel horizontally

7. Jan 1, 2007

### billiards

Well unless there's some highly unusaul morphology going on, it's pretty safe to say the (vertical) distance between the base of the cliff and where the stone lands would be 0.

I presume you're looking for horizontal distance in which case I'll give you a clue, s=d/t.